Neutron activation
Neutron activation is a process in which materials become radioactive through neutron radiation .
The nuclear reaction on which activation is based is usually the capture of a thermal neutron . The next heavier isotope of the element in question is in many cases radioactive. Other nuclear reactions - mostly triggered by fast neutrons - can lead to radioactive product nuclei. Due to the half-life and the energy spectrum of their gamma radiation (see gamma spectroscopy ), these radionuclides can be determined qualitatively and quantitatively.
If components that are exposed to a high neutron flux (e.g. in nuclear fission and fusion reactors ) have to be replaced due to radiation damage , they are usually treated as radioactive waste because of the neutron activation . When selecting the material for such components, it is important to consider the capture cross-section , but also the type of radiation and half-life of the radionuclide produced.
Use cases / examples
- The z. B. neutron activation caused in an aluminum foil can be used to detect free neutrons. Even ball measurement systems in nuclear reactors use neutron activation.
- The sustained radiation after an atomic bomb explosion is mainly due to the neutron activation of the material in the explosion area.
- The neutron activation is used for the detection of trace elements (see neutron activation analysis ). To do this, taking or even dissolving a sample is unnecessary. The method can therefore also be used for objects that must not be damaged (e.g. valuable works of art). The object becomes radioactive, but this activity can usually be kept very low. In this sense, neutron activation is a non-destructive analysis method . The limit of detection is specific to each element; for iron it is 10 −7 g, for gold 10 −13 g.